1. Field of the Invention
The present invention relates to a device which performs by a pneumatic-hydraulic booster the supply and discharge of a pressure oil in a hydraulic actuation chamber for the cushion-knockout mechanism associated with the slide of a press-machine such as a mechanical press, an oil hydraulic press and the like, and particularly to a pneumatic-hydraulic booster type driving device which is utilized for holding down a work plate such as a printed board and the like under the cushion operation thereof at the time of pressing as well as for knocking out the work plate from punches after the pressing respectively by predetermined pressures in the hydraulic actuation chamber.
The basic construction of such a pneumatic-hydraulic booster type driving device will be described hereinafter.
As shown in schematic views of FIGS. 7 through 9, a pneumatic-hydraulic booster 4 comprises a pneumatic cylinder 2 of a large diameter accommodating a piston 8 and an oil hydraulic cylinder 3 of a small diameter accommodating a plunger 17 connected thereto 8. The hydraulic cylinder 3 has a plunger chamber 3a which is adapted to be connected to a pressure oil inlet outlet/port 25 through a valve chamber 22, a valve seat 23 and an outlet chamber 24 arranged in order. The valve chamber 22 is provided with a valve unit 27 which is adapted to be opened in a state of a large flow area by a cushion actuating pressure in a cushion cylinder 63 of the press-machine so as to allow a high speed flow of a cushion pressure oil into the plunger chamber 3a through the pressure oil inlet outlet/port 25 and also to be opened in a state of a small flow area by a knockout actuator 28 so as to allow a flow out of a knockout pressure oil from the plunger chamber 3a to the pressure oil inlet outlet port 25.
The basic construction is utilized, for example, as shown in FIGS. 2 and 6.
A cushion knockout mechanism 62 is mounted to a slide 61 of a press-machine 60 so as to be driven vertically integratedly with the slide 61. When a crankshaft goes through the rotational phase of, for example 30.degree.-135.degree. (a cushion pre-pressurization A) during the descendant actuation stroke, a work fixation plate 67 is lowered to a lower position under punches 68 through a knockout transmission plate 65 and knockout pins 66 by pre-pressurizing a cushion of pressurized oil in an oil hydraulic actuation chamber 64 of a cushion cylinder 63 by means of a pneumatic-hydraulic booster type driving device 1.
When the crankshaft goes through the rotational phase of 135.degree.-180.degree. (a cushion operation B), the work fixation plate 67 is adapted to abut to the work plate 70 placed on a lower die 69. Thereupon, the pressure oil in the oil hydraulic actuation chamber 64 serves a cushion operation so that the fixation plate 67 fixes the work plate 70 under a cushioned condition without causing any damage to the work plate 70. Then the punches 68 continuously move on towards the underside of the work fixation plate 67 so as to punch the work plate 70.
When the slide 61 reaches the bottom dead center thereof, the work plate 70 gets frictionally engaged with the punches 68 in then punched through condition.
When the crankshaft takes the rotational phase of 180.degree.-270.degree. (a low pressure keeping C) during the ascendant return stroke of the slide 61, the work plate 70 is raised by the punches 68 in a frictionally engaged condition.
When the crankshaft reaches the rotational phase of 270.degree. (a knockout operation D), the work plate 70 is knocked out from the punches 68 through the work fixation plate 67 which is actuated through the knockout pins 66 by supplying a knockout pressure to the oil hydraulic actuation chamber 64 by means of the pneumatic-hydraulic booster type driving device 1.
After that, when the crankshaft goes through the rotational phase of 315.degree.-30.degree. (a pressure reduction operation E), the pressure in the oil hydraulic actuation chamber 64 is reduced to the cushion pre-pressurized oil pressure and one cycle of the punching work is completed.
During the operation of the cushion-knockout mechanism 62, the pneumatic-hydraulic booster type driving device 1 is adapted to operate in such a manner as shown in FIGS. 7 through 9.
In the cushion pre-pressurizing condition (A), as shown in FIG. 7, a supply of high pressure air is supplied to both the high pressure actuation chamber 9 and the low pressure actuation chamber 10 of the pneumatic cylinder 2 and the output portion 54 of the knockout actuator 28 caused to recede so that the pressures in the plunger chamber 3a and in the oil hydraulic actuation chamber 64 of the cushion cylinder 63 are kept at a low pressure. By this low cushion pre-pressurized pressure, the knockout transmission plate 65 is adapted to be pushed downwardly.
In the cushion operating condition (B), as shown in FIG. 8, when the knockout transmission plate 65 is subjected to a load of a work reaction force (R), the pressure oil in the oil hydraulic actuation chamber 64 serves to open the valve body 30 in a large flow area so as to flow into the plunger chamber 3a quickly and serves to push and hold down the work plate 70 stably while allowing an upward movement of the knockout transmission plate 65 as a cushion operation thereof.
In the knockout operating condition (D), as shown in FIG. 9, when only the high pressure actuation chamber 9 of the pneumatic cylinder 2 is supplied with a pressure air so as to increase the pressure in the plunger chamber 3a and then the output portion 54 of the knockout actuator 28 is extended so as to open the valve body 30 in a small flow area, a small amount of a high pressure oil is supplied from the plunger chamber 3a to the oil hydraulic actuation chamber 64 so that the knockout transmission plate 65 serves to knock out the work plate 70 strongly at a low speed.
2. Background of the Prior Art
In the above-mentioned basic construction, the inventor of the present invention previously proposed the structure shown in FIG. 10 or in FIG. 11 (refer to Japanese Utility Model Provisional Publication No. 76348 of 1983) as a construction for the practical applications of the valve unit 27 and the knockout actuator 28.
In the first conventional embodiment, as shown in FIG. 10, the symbol 103 is an oil hydraulic cylinder, 103a is a plunger chamber, 124 is an outlet chamber, 125 is a pressure oil inlet outlet port, and 127 is a valve unit. There is provided a single valve body 130 in the valve chamber 122 and there is provided a valve closing spring 131 between the valve body 130 and the end wall 133 of the the valve chamber 122, opposed to the valve seat 123 so that the valve body 130 is pushed to the valve seat 123 by the resultant force of the resilient force of the valve closing spring 131 and the pressure in the valve chamber 122. The output portion 154 of the knockout actuator 128 is disposed oppositely to the valve body 130 so as to enable to push and open the valve body 130.
In the second conventional embodiment, as shown in FIG. 11, the above-mentioned first embodiment is improved as follows component parts having the same function are indicated by the same symbol as one shown in FIG. 10. That is, the valve body 130 is provided with a knockout oil supply hole 180 which connects the plunger chamber 103a to the outlet chamber 124 and has a knockout valve body 181 of a small diameter fitted therein 180. There is provided a valve closing spring 182 between the knockout oil supply hole 180 and the knockout valve body 181. The output portion 154 of the knockout actuator 128 is disposed oppositely to the knockout valve body 181 so as to push and open the valve body 181.
FIG. 11 may be compared to FIG. 7, in that each shows the respective valve body (30 in FIG. 7, 130 in FIG. 11) in a comparable seated position. As persons skilled in the art will appreciate, when protruding output portion 154 is moved upward by knockout activator 128, the former will lift knockout body 181. High pressure oil from chamber 103a will then flow downward through hole 180 in valve body 130, through knockout valve body 181, past the upper end of 154 and into outlet chamber 124.
There are, however, a number of disadvantages associated with the above-mentioned first conventional embodiment (refer to FIG. 10).
(1) The knockout actuator 128 becomes large in size.
During the knockout operation, the output portion 154 of the knockout actuator 128 is adapted to push and open the valve body 130 after increasing the pressures in the plunger chamber 103a and in the valve chamber 122 in advance.
Thereupon, since the valve body 130 is subjected to a large valve opening force in accordance with the large flow area defined by the diameter d.sub.0 ' of the valve seat by the pressure in the valve chamber 122, a large knockout actuation force is required and consequently the knockout actuator 128 should become large.
(2) The durability of the valve closing spring 131 suffers.
During the cushion operation and during the knockout operation, since the valve closing spring 131 is vibrated by the pressure oil flowing through the valve chamber 122, it gets fatigued and degraded in a short time.
On the other hand, the second conventional embodiment (refer to FIG. 11) has the advantage that (1) because the knockout actuator 128 can be made smaller in size due to the small knockout actuation force in accordance with the small flow area defined by the valve seat diameter d.sub.3 of the knockout valve body 181. However, besides the above-mentioned disadvantage (2) still unsolved therein, moreover there are following disadvantages (3), (4) associated therewith.
(3) The construction of the valve unit 127 is complicated.
Since there are provided two valve bodies 130, 181 and two valve closing springs 131, 182 therein, the parts number gets increased and the construction gets more complicated.
(4) Pressurized oil tends to leak out.
Since the valve opens and closes at two locations, pressurized oil tends to leak out due to foreign substances caught therein.